1. Field of the Invention
The present invention relates to a surveying instrument, and more specifically, to a survey point indicating instrument, provided in a surveying instrument, for indicating a survey point so that the direction of a line of sight can be recognized visually from the side of the target.
2. Description of the Related Art
FIG. 3 shows a diagrammatic representation of a conventional survey point indicating instrument (first conventional survey point indicating instrument) for indicating a survey point. This survey point indicating instrument has a translucent plate 27 having different colors which is positioned on the optical axis of a collimating lens 25 at a focal point thereof. A light source 23 is disposed behind the translucent plate 27. Primary light rays emitted from the light source 23 are diffused as secondary light rays through the translucent plate 27, and are subsequently collimated through the collimating lens 25 to eventually reach a target.
In such a conventional survey point indicating instrument, if the collimated light rays that travel toward the target are viewed from the target side with a half of the translucent plate 27 above the optical axis of the collimating lens 25 colored green and the other half of the translucent plate 27 below the optical axis of the collimating lens 25 colored red, a mixture of red and green colors is viewed in the vicinity of the optical axis of the collimating lens since the collimated light rays are red and green on right and left sides of the optical axis of the collimating lens, respectively. Namely, red light is seen on the left side of the optical axis of the survey point indicating instrument, green light is seen on the right side of the optical axis of the survey point indicating instrument, and a mixture of red and green lights is seen in the vicinity of the optical axis of the survey point indicating instrument.
In this conventional survey point indicating instrument, the light emitted from the light source 23 toward the target can easily be recognized visually because the light source 23 can be viewed having a certain range of width.
However, in the first conventional survey point indicating instrument, no light rays emitted from the light source 23 are directly viewed, only secondary light rays that are passed through the translucent plate 27 are viewed by a surveyor. Accordingly, a high-intensity light source must be used to serve as the light source 23 when the light emitted therefrom is viewed from a great distance, which inevitably increases power consumption.
FIG. 4 shows a diagrammatic representation of another conventional survey point indicating instrument (second conventional survey point indicating instrument) for indicating a survey point which is disclosed in Japanese laid-open utility model publication No.62-10615. In this conventional survey point indicating instrument, two bundles of light rays emitted from two LEDs 33 are reflected by two reflecting surfaces of a prism 37 to be projected toward a target via a collimating lens 35. The prism 37 is positioned on the optical axis of the collimating lens 35. In the second conventional survey point indicating instrument, a survey point can be indicated by primary light rays, not secondary light rays, since the survey point indicating instrument uses no translucent plate such as the translucent plate 27 shown in FIG. 3. Accordingly, the light rays emitted from the two LEDs 33 toward the target can easily be recognized visually even from a great distance. Moreover, unlike the first conventional survey point indicating instrument shown in FIG. 3, not only a survey point can be indicated by primary light rays, but also a collimating lens does not have to be provided for each light source in the second conventional survey point indicating instrument.
However, it is necessary to provide the second conventional survey point indicating instrument with a prism (the prism 37) having two reflecting surfaces. This is a cause of increasing the cost of production.
FIG. 5 shows a diagrammatic representation of another conventional survey point indicating instrument (third conventional survey point indicating instrument) for indicating a survey point which is disclosed in Japanese patent No.3096140. This conventional survey point indicating instrument is provided with two collimating lenses 45, two light sources 43 and two light shield plates 47. The optical axes of the two collimating lenses 45 extend parallel to each other. The two light sources 43 are positioned on the optical axes of the two collimating lenses 45, respectively, and each light source 43 emits visible light rays. Each of the two light shield plates 47 is positioned at the back focal point (focal point on the light source 43 side) of the associated collimating lens 45 to cut off the light rays which are emitted from the associated light source 43 to prevent the light rays from traveling outside the area between the parallel optical axes of the two collimating lenses 45. Due to this optical arrangement, although light rays emitted from each light source 43 to proceed toward the associated collimating lens 45 are half cut off by the associated light shield plate 47, the remaining half of the light rays reach the associated collimating lens 45 without being diffused, unlike the first conventional survey point indicating instrument. Accordingly, the light emitted from each light source 43 toward the target can easily be recognized visually even from a great distance. Additionally, there is no need to provide the survey point indicating instrument with a prism (the prism 37) having two reflecting surfaces, unlike the second conventional survey point indicating instrument shown in FIG. 4.
However, the third conventional survey point indicating instrument shown in FIG. 5 must be provided with two survey point indicating instrument lenses (the survey point indicating instrument lenses 45), even though a survey point can be directly indicated by primary light rays emitted from each light source 43. This is a cause of increasing the cost of production.
The present invention provides a low-cost and low-power-consumption survey point indicating instrument, provided in a surveying instrument, for indicating a survey point so that the direction of a line of sight can be easily recognized visually from the target side, even from a long distance.
According to an aspect of the present invention, a survey point indicating instrument is provided for recognizing a collimation direction visually, the survey point indicating instrument including a collimating lens; two light sources positioned so that optical axes of the two light sources intersect each other on an optical axis of the collimating lens at a focal point of the collimating lens; a driving circuit for controlling light emissions of the two light sources independently from each other; and a light shield plate having a slit, and positioned between the focal point and the two light sources so that light rays emitted from each of the two light sources to travel in an area between the optical axes are allowed to pass through the slit while other light rays emitted from each of the two light sources are cut off by the light shield plate to prevent the other light rays from traveling outside the area between the optical axes.
It is desirable for the driving circuit to control the light emissions of the two light sources so that the two light sources flash periodically at different frequencies.
It is desirable for the two light sources to emit different colored lights.
It is desirable for the two light sources to emit red light and green light, respectively.
Among light rays which are passed through the slit to intersect each other at the focal point, it is desirable for light rays thereof incident on a central portion of the collimating lens to be collimated thereby to travel as a parallel light beam after passing through the collimating lens, while other light rays thereof incident on a peripheral portion of the collimating lens to firstly converge after passing through the collimating lens, and to subsequently diverge.
It is desirable for each of the two light sources to be an LED.
According to another embodiment, a survey point indicating instrument is provided, including a collimating lens; two light sources positioned behind the collimating lens so that optical axes of the two light sources intersect each other on an optical axis of the collimating lens at a back focal point of the collimating lens; a light shielding device, positioned between the collimating lens and the two light sources, for cutting off light rays emitted from each of the two light sources to prevent light rays from traveling outside an area between the optical axes, and for allowing the light rays emitted from each of the two light sources to travel within the area to pass therethrough; and a driving circuit for controlling light emissions of the two light sources independently from each other.
It is desirable for the light shielding device to include a light shield plate positioned between the back focal point of the collimating lens and the two light sources.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2002-240297 (filed on Aug. 21, 2002) and No.2002-248318 (filed on Aug. 28, 2002) which are expressly incorporated herein by reference in their entireties.